The present invention relates to devices and methods for dispensing or receiving a liquid volume, and in particular to devices and methods which enable a precise dosing of a liquid volume.
From standard technology, different dosing systems are known, wherein a difference may be made between dosing systems for continuous delivery and open-jet dosing systems.
Those dosing systems may be referred to as dosing systems for a continuous delivery which can deliver liquids in a closed system, if applicable also against a counter-pressure acting at the output or dispensing position. Such systems may also deliver discrete volumes by a time control. Examples of such systems are perfusor pumps, insulin pumps, fuel pumps, etc.
DE 10 2008 053 411 A1 describes a pressure-driven dosing system, wherein a flow sensor is used in order to monitor the amount of fuel gas in a storage reservoir which flows out after dosing and thus possibly to regulate dosing by switching a dosing valve. In addition, a pressure sensor may be provided to support the determination of an air volume streaming from a pressure source to the storage reservoir.
From WO 96/11024 A1, a continuous dosing system is known which is based on the drive of a liquid by a disposable syringe pump. As a measured value according to WO 96/11024 A1, the position of a syringe piston of the syringe pump is used which is determined by a sensor at the proximal end of the same. Alternatively, it is known from U.S. Pat. No. 6,656,148 B2 to consider the force necessitated for moving the piston of a syringe pump as a sensor variable. As the force determined at the piston also contains portions of frictional forces of the piston drive which may be unknown and variable, the method described herein may be inaccurate.
From U.S. Pat. No. 6,830,558 B2, an infusion device is known wherein a pressure sensor is provided to be able to detect flow conditions, for example the closing of a flow path or an inadequate flow within the flow path.
In contrast to dosing systems for a continuous delivery, open-jet dosing systems enable the dosing of liquids as freely flowing liquid drops or liquid jets through the air. Such systems may in particular be utilized in a volume range of less than 1 μl. Typical examples here are systems based on the ink-jet principle, systems wherein dispensing or outputting a pressurized liquid is controlled by dosing valves, or systems wherein liquid is dispensed by squeezing a tube. Different methods are known here to determine the dosed volumes or to monitor and regulate dosing.
Here, frequently small sensor units are used which do not influence the dosing process and allow a monitoring of the process or regulation of the dosed amount in real time (online method).
Thus, EP 1347152 B1 discloses a method based on continuous measurements of the flow rate in a supply channel of a nozzle. From the measured flow rate, by temporal integration, the dispensed liquid amount may be calculated. A substantial disadvantage of such systems is, however, that the mass flow sensors have to be individually calibrated to each liquid used and cannot be used as disposable products due to the expensive sensors.
Other methods, wherein sensors integrated into the supply line to a nozzle allow information to be given about dosed volumes on the basis of impedance measurements, pH value measurements or conductivity measurements, are, for example, known from WO 2005/121780 A2. Such sensors serve for monitoring the dosing process and documenting its quality.
Further, methods are known from standard technology, wherein dosed liquid amounts are not determined by internal sensors before leaving the nozzle but only after being dispensed from the dosing unit. The information thereby gained may be utilized to have a controlling or regulating effect on the process and thus increase its precision. In this respect, reference is made, for example, to US 2009/0055131 A1. Regulations relating to this known method refer to sensors which may determine the volume of the dosed liquid in order to actively adapt the dosing to the desired target volume based on the sensor data. For example, according to JP 2004-251818 A, such a method is based on a volume measurement of individual applied drops which is used to readjust the number and the drop volume of the subsequent dosing operations and thus be able to adapt the overall volume dispensed in many individual drops more precisely to the set value.
Further, pipetting systems are known which keep the pressure boundary conditions in a dosing system constant using integrated pressure sensors by means of active regulation or controlling. In this way, dispensing a liquid amount under constant known conditions may be guaranteed, see, for example, U.S. Pat. No. 5,723,795 and U.S. Pat. No. 4,675,301. It is further known from DE 602005002918 T2 to use integrated pressure sensors to execute a liquid level detection. This method serves for determining the liquid level in a sample cavity which only has an indirect influence on the dosing volume, however.